scripts: build: gen_isr: irq more than 1 byte per level

In some architectures such as RISC-V it can be the case that
there are more than 255 interrupts per level. Additionally,
this short comming is not completely solved by simply adding
additional levels or aggrigators. This diff adds the ability
to determine how many bits are needed per level based on the
MAX_IRQ_PER_AGGRIGATOR Kconfig variable.

Signed-off-by: Joshua Lilly <jgl@meta.com>

scripts/build/gen_isr_tables.py

@@ -25,7 +25,9 @@
 #              into 1 line which then goes into the 2nd level)
 FIRST_LVL_INTERRUPTS = 0x000000FF
 SECND_LVL_INTERRUPTS = 0x0000FF00
+SECND_LVL_SHIFT = 8
 THIRD_LVL_INTERRUPTS = 0x00FF0000
+THIRD_LVL_SHIFT = 16
 
 def debug(text):
     if args.debug:
@@ -231,6 +233,12 @@ def getindex(irq, irq_aggregator_pos):
               " Recheck interrupt configuration.")
 
 def main():
+    global FIRST_LVL_INTERRUPTS
+    global SECND_LVL_INTERRUPTS
+    global SECND_LVL_SHIFT
+    global THIRD_LVL_INTERRUPTS
+    global THIRD_LVL_SHIFT
+
     parse_args()
 
     with open(args.kernel, "rb") as fp:
@@ -240,13 +248,26 @@ def main():
     if "CONFIG_MULTI_LEVEL_INTERRUPTS" in syms:
         max_irq_per = syms["CONFIG_MAX_IRQ_PER_AGGREGATOR"]
 
+        # if more than 255 interrupts are allowed by the CPU
+        # per level then we need to recalculate the bit masks 
+        bits = max_irq_per.bit_length()
+        if bits > 8:
+            FIRST_LVL_INTERRUPTS = 0
+            for i in range(0, bits):
+                FIRST_LVL_INTERRUPTS = (FIRST_LEVEL_MASK << 1) | 1
+
         if "CONFIG_2ND_LEVEL_INTERRUPTS" in syms:
             num_aggregators = syms["CONFIG_NUM_2ND_LEVEL_AGGREGATORS"]
             irq2_baseoffset = syms["CONFIG_2ND_LVL_ISR_TBL_OFFSET"]
             list_2nd_lvl_offsets = [syms['CONFIG_2ND_LVL_INTR_{}_OFFSET'.
                                          format(str(i).zfill(2))] for i in
                                     range(num_aggregators)]
-
+            if bits > 8 and 2 * bits < 32:
+                SECND_LVL_SHIFT += (bits - SECND_LVL_SHIFT)
+                SECND_LVL_INTERRUPTS = FIRST_LVL_INTERRUPTS << SECND_LVL_SHIFT
+            else if 2 * bits >= 32:
+                error("MAX_IRQ_PER_AGGREGATOR is too large to have second tier interrupts.")
+
             debug('2nd level offsets: {}'.format(list_2nd_lvl_offsets))
 
             if "CONFIG_3RD_LEVEL_INTERRUPTS" in syms:
@@ -256,6 +277,12 @@ def main():
                                              format(str(i).zfill(2))] for i in
                                         range(num_aggregators)]
 
+            if bits > 8 and 3 * bits < 32:
+                THIRD_LVL_SHIFT = 2 * SECND_LVL_SHIFT
+                THIRD_LVL_INTERRUPTS = FIRST_LVL_INTERRUPTS << THIRD_LVL_SHIFT
+            else if 3 * bits >= 32:
+                error("MAX_IRQ_PER_AGGREGATOR is too large to have third tier interrupts.")
+
                 debug('3rd level offsets: {}'.format(list_3rd_lvl_offsets))
 
     intlist = read_intlist(args.intlist, syms)
@@ -311,8 +338,8 @@ def main():
             else:
                 # Figure out third level interrupt position
                 debug('IRQ = ' + hex(irq))
-                irq3 = (irq & THIRD_LVL_INTERRUPTS) >> 16
-                irq2 = (irq & SECND_LVL_INTERRUPTS) >> 8
+                irq3 = (irq & THIRD_LVL_INTERRUPTS) >> THIRD_LVL_SHIFT
+                irq2 = (irq & SECND_LVL_INTERRUPTS) >> SECND_LVL_SHIFT
                 irq1 = irq & FIRST_LVL_INTERRUPTS
 
                 if irq3: